High-speed data communication integrated circuit (IC) dies are known to include both drivers and receivers. The drivers of one such IC connect to respective receivers on another via one or more signal transmission lines. ICs that include drivers and receivers also include termination elements that attempt to match the characteristic impedance of transmission lines to the output impedance of the associated driver and input impedance of the associated receiver. This matching is important, as impedance mismatches degrade signal quality and consequently reduce communication speed and reliability.
Some conventional communication systems employ control systems that calibrate the impedance of on-die termination (ODT) elements for improved impedance matching. For a detailed discussion of one such system, see U.S. Pat. No. 6,418,500 entitled “Feedback Control for Termination Adjustment,” which issued on Jul. 9, 2002, to Gai et al. The system described by Gai et al. works well in many applications. Still, high-speed data communication circuits must achieve ever-greater performance levels, at competitive prices, to satisfy customer demand. There is therefore a need for area- and power-efficient ODT systems that facilitate improved data communication circuit performance.